U.S. patent number 10,175,306 [Application Number 15/366,330] was granted by the patent office on 2019-01-08 for large area magnetic flux sensor.
This patent grant is currently assigned to The United States of America, as represented by the Secretary of the Navy. The grantee listed for this patent is John E. Miesner. Invention is credited to John E. Miesner.
United States Patent |
10,175,306 |
Miesner |
January 8, 2019 |
Large area magnetic flux sensor
Abstract
An exemplary magnetic flux sensor in accordance with the present
invention is characterized by an electrical output that is
proportional to the total static and dynamic flux passing normally
through a large area. An oscillating electrical current passing
down a conducting area produces Lorentz forces, which are
transferred to piezoelectric areas. The piezoelectric areas produce
electrical voltage at the oscillation frequency whereby amplitude
is proportional to the total magnetic flux passing normally through
the conducting area. Demodulating the voltage provides an
electrical signal with high sensitivity, dynamic range, and noise
immunity.
Inventors: |
Miesner; John E. (Fairfax,
VA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Miesner; John E. |
Fairfax |
VA |
US |
|
|
Assignee: |
The United States of America, as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
64815658 |
Appl.
No.: |
15/366,330 |
Filed: |
December 1, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R
33/072 (20130101); G01R 33/028 (20130101) |
Current International
Class: |
G01R
33/02 (20060101); G01R 33/028 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; Thang
Attorney, Agent or Firm: Kaiser; Howard
Government Interests
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without payment of any royalties thereon or therefor.
Claims
What is claimed is:
1. A magnetic flux sensing apparatus comprising: an electrically
conductive member; a pair of piezoelectric members adjoining said
electrically conductive member on opposite sides of said
electrically conductive member; a pair of springs for exerting
tensile stress on the respective said pair of piezoelectric members
in opposite directions away from said electrically conductive
member; an electrical current generator for sending current to said
electrically conductive member, wherein said current flows through
said electrically conductive member to produce voltages in the
respective said pair of piezoelectric members that are indicative
of a total magnetic flux through said electrically conductive
member.
2. The magnetic flux sensing apparatus of claim 1, further
comprising a computer for calculating said total magnetic flux
based on said voltages.
3. A magnetic flux sensing device comprising: a sensing sheet, said
sensing sheet characterized by a length and a width and including a
current-conducting portion, a first piezoelectric portion, and a
second piezoelectric portion, said current-conducting portion, said
first piezoelectric portion, and said piezoelectric portion
extending said length, said first piezoelectric portion and said
second piezoelectric portion located at widthwise opposite sides of
said current-conducting portion; at least one first spring for
exerting a first tension, said first tension exerted on said first
piezoelectric portion in a first widthwise direction; at least one
second spring for exerting a second tension, said second tension
exerted on said second piezoelectric portion in a second widthwise
direction, said first widthwise direction and said second widthwise
direction being opposite each other.
4. The magnetic flux sensing device of claim 3, further comprising:
a first pair of electrodes, each of said first pair of electrodes
including a metallic film, said first piezoelectric portion having
a first top piezoelectric surface and a first bottom piezoelectric
surface, said first pair of electrodes contiguously covering,
respectively, said first top piezoelectric surface and said first
bottom piezoelectric surface; a second pair of electrodes, each of
said second pair of electrodes including a metallic film, said
second piezoelectric portion having a second top piezoelectric
surface and a second bottom piezoelectric surface, said second pair
of electrodes contiguously covering, respectively, said second top
piezoelectric surface and said second bottom piezoelectric
surface.
5. The magnetic flux sensing device of claim 4, wherein when an
oscillating current is caused to flow through said
current-conducting portion in a lengthwise direction, said
oscillating current produces Lorentz forces that affect said first
piezoelectric portion and said second piezoelectric portion,
resulting in voltages on said first pair of electrodes and said
second pair of electrodes that are indicative of a total magnetic
flux through said current-conducting portion.
6. The magnetic flux sensing device of claim 5, wherein said
oscillating current is uniform across said width.
7. The magnetic flux sensing device of claim 5, wherein: the
magnetic flux sensing device further comprises a casing for said
sensing sheet, said at least one first spring, said at least one
second spring, said first pair of electrodes, and said second pair
of electrodes; said at least one first spring, said at least one
second spring, and said case are components of a mechanical
isolation system for said sensing sheet whereby vibrations in said
casing are attenuated by a mass-spring system before passing to
said sensing sheet.
8. The magnetic flux sensing device of claim 5, further comprising
an oscillator, for producing a waveform signal.
9. The magnetic flux sensing device of claim 8, further comprising
a current amplifier, for amplifying said waveform signal to produce
said oscillating current.
10. The magnetic flux sensing device of claim 8, further comprising
a sense amplifier, for amplifying said voltages on said first pair
of electrodes and said second pair of electrodes, said amplifier
producing a voltage signal.
11. The magnetic flux sensing device of claim 10, further
comprising a demodulator, for: receiving the amplified voltage
signal from said sense amplifier; receiving said waveform signal
from said oscillator; producing an output voltage signal that is
proportional to said total magnetic flux through said
current-conducting portion.
12. The magnetic flux sensing device of claim 10, further
comprising a computer for communicating with said demodulator and
processing said output voltage signal.
13. A method for sensing magnetic flux, the method comprising:
providing a sensing sheet, said sensing sheet characterized by a
length and a width and including a current-conducting portion, a
first piezoelectric portion, and a second piezoelectric portion,
said current-conducting portion, said first piezoelectric portion,
and said piezoelectric portion extending said length, said first
piezoelectric portion and said second piezoelectric portion located
at widthwise opposite sides of said current-conducting portion;
exerting a first tension with respect to said sensing sheet, said
exerting of said first tension including using at least one first
spring, said first tension exerted on said first piezoelectric
portion in a first widthwise direction; exerting a second tension
with respect to said sensing sheet, said exerting of said second
tension including using at least one second spring, said second
tension exerted on said second piezoelectric portion in a second
widthwise direction, said first widthwise direction and said second
widthwise direction being opposite each other; causing an
oscillating current to flow through said current-conducting portion
in a lengthwise direction, wherein said oscillating current
produces Lorentz forces that affect said first piezoelectric
portion and said second piezoelectric portion, resulting in a first
electrode voltage and a second electrode voltage, said first
electrode voltage being on said first piezoelectric portion, said
second electrode voltage being on said second piezoelectric
portion, wherein said first electrode voltage and said second
electrode voltage are indicative of a total magnetic flux through
said current-conducting portion.
14. The method for sensing magnetic flux of claim 13, wherein said
oscillating current is uniform across said width.
15. The method for sensing magnetic flux of claim 13, further
comprising associating an outer case with said sensing sheet, said
at least one first spring, and said at least one second spring,
wherein said at least one first spring, said at least one second
spring, and said case are components of a mechanical isolation
system for said sensing sheet whereby vibrations in said outer case
are attenuated by a mass-spring system before passing to said
sensing sheet.
16. The method for sensing magnetic flux of claim 13, further
comprising: producing a waveform signal; amplifying said waveform
signal to produce said oscillating current; producing a voltage
signal, said producing of said voltage signal including amplifying
said voltages on said first pair of electrodes and said second pair
of electrodes.
17. The method for sensing magnetic flux of claim 16, wherein: said
producing of said waveform signal includes using an oscillator;
said amplifying of said waveform signal includes using a current
amplifier; said producing of said voltage signal includes using a
sense amplifier.
18. The method for sensing magnetic flux of claim 16, further
comprising producing an output voltage signal that is proportional
to said total magnetic flux through said current-conducting
portion, wherein said output voltage is based on said waveform
signal and said voltage signal.
19. The method for sensing magnetic flux of claim 18, wherein: said
producing of said waveform signal includes using an oscillator;
said amplifying of said waveform signal includes using a current
amplifier; said producing of said voltage signal includes using a
sense amplifier; said producing of said output voltage includes
using a demodulator.
20. The method for sensing magnetic flux of claim 18, further
comprising using a computer for processing said output signal,
wherein said computer communicates with said demodulator.
21. The method for sensing magnetic flux of claim 13, further
comprising combining in a circuit said first electrode voltage and
said second electrode voltage, said first electrode voltage being
on said first piezoelectric portion, said second electrode voltage
being on said second piezoelectric portion, said combining in said
circuit being performed such that: transverse forces due to a
magnetic field will add together and thereby increase a total
voltage; and noise sources will cancel together and thereby not
increase said total voltage.
22. The method for sensing magnetic flux of claim 21, wherein said
circuit is a series circuit.
23. The method for sensing magnetic flux of claim 21, wherein said
circuit is an anti-parallel circuit.
Description
BACKGROUND OF THE INVENTION
The present invention relates to magnetic flux sensors, more
particularly to magnetic flux sensors suitable for sensing magnetic
flux through relatively large areas.
There currently exists no practical method to measure the total
static and dynamic magnetic flux passing normally through a large
area. Semiconductor Hall devices are commonly used in magnetic
machines, but they are small and essentially sample a single point.
Magnetoresistive devices are becoming more practical; however, they
are small and they sense flux down the device axis and not though
the sensor thickness.
Many devices would benefit from a large area magnetic flux sensor.
For example, an electrodynamic actuator produces forces
proportional to the current through the coil conductors and the
total flux perpendicular to the coil surface. Typically the coil is
designed to be wider than optimum to keep the flux within the area
of the coil as it moves, and to thereby reduce force dependence on
position. If the total flux perpendicular to the entire coil
surface were known, then the conductor current could be controlled
to eliminate the force dependence on position. This would allow the
coil width to be optimized for more efficient actuator
operation.
U.S. Pat. No. 6,975,109 to Bo Su Chen discloses a microelectronic
sensor that uses the Lorentz force and a piezoelectric effect to
measure magnetic flux. A direct current is passed through a first
layer, and the resulting Lorentz force causes shear in a
piezoelectric second layer, which produces a voltage proportional
to the magnetic flux. It should be appreciated that the device
disclosed by Chen is not capable of continuously measuring a static
or slowly varying magnetic flux. A statically induced piezoelectric
voltage will dissipate with time, and stray electrical charge noise
will build up in the detection circuit and degrade the flux
measurement accuracy of Chen's device. Also, the construction
methods of the apparatus disclosed by Chen limits its use to a
small area. Finally, Chen's device will have a low sensitivity,
because piezoelectric materials have a greatly reduced voltage
response to shear as compared to extension modes.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention
to provide a magnetic flux sensor that detects total normal static
and dynamic flux through an arbitrarily large area. It is a further
object to provide a magnetic flux sensor with high sensitivity,
dynamic range, and noise immunity.
An exemplary embodiment of a magnetic flux sensing apparatus in
accordance with the present invention comprises an electrically
conductive member, a pair of piezoelectric members, a pair of
tensioning mechanisms, and an electrical current generator. The two
piezoelectric members adjoin the conductive member on opposite
sides of the conductive member. The two tensioning mechanisms exert
tensile stress on the respective piezoelectric members in opposite
directions away from the conductive member. The electrical current
generator sends current to the conductive member. The current flows
through the conductive member and interacts with the present
magnetic field to produce transverse forces on the piezoelectric
members causing relative voltage between their top and bottom
electrodes. The voltages produced are indicative of a total
magnetic flux through the conductive member.
Exemplary practice of the present invention provides a magnetic
flux sensor with output proportional to the total normal magnetic
flux, both static and dynamic, over a large area. An exemplary
magnetic flux sensor of the present invention includes a current
conducting area with width W, length L, and thickness t. An
oscillating current of amplitude I that is uniform across the width
W flows down the length L. Lorentz force F is produced proportional
to current I and total magnetic flux .PHI. through the area:
F=.PHI.I
The oscillating force is transferred to a left electroded
piezoelectric area and a right electroded piezoelectric area. Each
piezoelectric area is made of a material such as poled
Polyvinylidene Difluoride (PVDF). These forces cause transverse
stress S.sub.1 in the left and right piezoelectric areas equal to
the force divided by the cross-sectional area Lt
.PHI..times..times. ##EQU00001##
The piezoelectric areas produce voltage on their electrodes at the
oscillation frequency according to the piezoelectric effect. The
output voltage for transverse stress may be calculated using the
piezoelectric stress constant g.sub.31 by
V.sub.out=g.sub.31S.sub.1t
Substituting the above equation for transverse stress S.sub.1
results in:
.times..PHI. ##EQU00002##
Equally, in terms of the mean magnetic flux density B through the
area LW: V.sub.out=[WIg.sub.31]B
Therefore, the oscillating voltages on the respective electrodes of
the left and right piezoelectric areas have an amplitude that is
proportional to the total magnetic flux .PHI. or the mean magnetic
flux density B through the current conducting area.
The voltages from the left and right piezoelectric areas may be
combined in a series arrangement by connecting the left and right
bottom electrodes together and measuring the voltage difference
between the left and right top electrodes. Alternatively, the
voltages may be combined in an anti-parallel arrangement by
connecting the top electrode of each side to the bottom electrode
of the other side and then measuring the voltage difference between
the two electrode combinations. In either case, transverse forces
due to the magnetic field will produce opposite voltages on the
left and right piezoelectric areas which will add and increase the
measured output voltage. In contrast, most noise sources such as
air currents, vertical vibration, temperature changes, etc. will
produce voltages of the same polarity on the left and right
piezoelectric areas and therefore will cancel without producing
measured output voltage.
The large area magnetic flux sensor of the current invention is
only sensitive to normal magnetic fields, because magnetic flux
components in the plane of the current conducting area produce
forces that are normal to the plane, resulting in the same tension
changes in the both the left and right piezoelectric areas
producing cancelling voltage. The present invention's magnetic flux
sensor is likewise not sensitive to temperature changes,
self-Lorentz forces in the conducting area, and normal mechanical
vibrations, because these phenomena cause common voltage in the
left and right piezoelectric areas and are therefore cancelled.
The circuit with the series or anti-parallel left- and- right
piezoelectric areas is connected to a sense amplifier, which may be
a voltage or a charge amplifier. The circuit also may include a
resistor in parallel with the sense amplifier. The resistor acts as
a high pass filter when combined with the capacitance of the
piezoelectric areas. The resistor is chosen to attenuate voltage
output below the oscillation frequency.
The sense amplifier passes the voltage signal to a demodulator. The
demodulator output is the amplitude of the oscillating voltage from
the sense amplifier, which is proportional to the normal magnetic
flux .PHI. through the current conducting area as desired. To
obtain the highest noise rejection, the demodulator is preferably a
synchronous demodulator slaved to the oscillator producing the
current waveform. The demodulator is effectively a very sharp
filter rejecting noise at frequencies other than the oscillation
frequency and providing a low noise floor.
In exemplary practice of the present invention, the frequency of
current oscillation should preferably be high enough to effectively
reproduce the dynamic magnetic flux. According to the Nyquist
criteria, the oscillation frequency of the present invention should
be at least twice the highest frequency component of the changing
magnetic flux to be measured. Piezoelectric sheets, such as made of
poled PVDF, may be effectively used at 20 kHz or higher providing a
potential measurement bandwidth up to 10 kHz. The bandwidth may be
limited by a resonance of the current conducting area mass against
the stiffness of the sensing sheet. For high bandwidth operation,
the mass of the current conducting area should be as low as
practical.
Piezoelectric sheets, such as made of poled PVDF, provide a high
dynamic range and have been response-tested over fourteen orders of
magnitude. The dynamic range of the current invention is only
limited by the measurement electronics and the careful prevention
of noise contamination. Amplifiers with high dynamic range, in
particular charge amplifiers used with capacitive devices such as
piezoelectrics, are well known to those with ordinary skill in the
art.
The magnetic flux sensor of the present invention may include one
or more additional features to ensure high sensitivity, dynamic
range, and noise immunity. By way of example, one, some, or all of
the following features are possible in inventive practice: The
piezoelectric areas may be shielded by conductive bars in close
proximity to prevent contamination by the electromagnetic fields
from the current conducting area or from other sources. There may
be an enclosing conductive case that forms another layer of
shielding. There may be a magnetically transparent window covering
the conducting area to protect it and prevent impingement of air
currents. There may be a mass-spring suspension system to isolate
the sensing sheet from mechanical vibration. All cabling may be
shielded to prevent induced electromagnetic noise.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example,
with reference to the accompanying drawings, wherein like numbers
indicate same or similar parts or components, and wherein:
FIG. 1 illustrates an example of a possible area of interest for
performing magnetic flux measurement in accordance with the present
invention. As shown in FIG. 1, the magnetic flux density contours
are superimposed.
FIG. 2 is a plan view of an example of an inventive sensing sheet
that may be included in a magnetic flux sensor in accordance with
the present invention, such as the exemplary inventive embodiment
shown in FIG. 4 and FIG. 5.
FIG. 3 is an elevation view of the exemplary inventive sensing
sheet shown in FIG. 2. As shown in FIG. 2 and FIG. 3, each
functional area is identified.
FIG. 4 is an exploded perspective view of an exemplary embodiment
of a magnetic flux sensor in accordance with the present
invention.
FIG. 5 is a side cross-sectional view of the exemplary inventive
embodiment shown in FIG. 4.
FIG. 6 is a circuitry diagram of an exemplary embodiment of a
magnetic flux sensor in accordance with the present invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
Referring now to FIG. 1, shown is an exemplary area of interest 10,
characterized by width W and length L. Magnetic flux passes through
this area 10, and exemplary magnetic flux density contours are
shown as lines labeled B. The total normal magnetic flux .PHI. is
equal to B integrated over the area 10. There is no known method or
device to quickly and accurately measure the total normal magnetic
flux .PHI. passing through example area 10. Conventional sensors,
such as Hall sensors, would require numerous point measurements to
obtain enough data to accurately integrate B over the area.
An example of inventive practice is now described with reference to
FIG. 2, FIG. 3, FIG. 4 and FIG. 5. FIG. 2 and FIG. 3 show an
inventive sensing sheet 101 with various areas identified. Area
101a is the current conducting area; areas 101b and 101c are the
piezoelectric areas; areas 101f and 101g are the attachment areas;
and areas 101d and 101e are the bonding areas. Area 101a represents
the area of interest 10. Current I, with a uniform current density
across width W, flows down length L of current conducting area
101a. Current I interacts with magnetic flux through current
conducting area 101a to produce, at each point, a Lorentz force
proportional to the magnitude of the current and the magnetic flux
at that point. The Lorentz forces are transverse to the direction
of current flow and are transferred to piezoelectric areas 101b and
101c.
The entire sensing sheet 101 is held in transverse tension by
extensional forces applied to attachment areas 101f and 101g.
Transverse forces from current conducting area 101a will change the
tension in piezoelectric areas 101b and 101c in opposite
directions. For example, in the depiction of FIG. 2, forces to the
right will increase the tension in piezoelectric area 101b and
reduce the tension in piezoelectric area 101c. Piezoelectric areas
101b and 101c are electroded piezoelectric sheets.
Each of the two piezoelectric areas is contiguously sandwiched
between a corresponding pair of electrodes. Piezoelectric area 101b
is adjacently interposed between top electrode 101b.sub.TOP and
bottom electrode 101b.sub.BOT. Piezoelectric area 101c is
adjacently interposed between top electrode 101c.sub.TOP and bottom
electrode 101c.sub.BOT. Piezoelectric areas 101b and 101c produce
voltage on their respective top (upper) and bottom (lower)
electrodes in response to the changes in tension from current
conducting area 101a. The voltages will be in opposite directions
corresponding to the opposite changes in tension. For example, if a
force to the right causes piezoelectric area 101b to have a
positive voltage on the upper electrode 101b.sub.TOP, then it will
cause piezoelectric area 101c to have a negative voltage on the
upper electrode 101c.sub.TOP.
Many methods of manufacture are available to produce sensing sheet
101 with the requisite areas and properties. For example, one could
use a single sheet of poled PVDF with continuous metal film on the
top and bottom surface as the starting material, and then remove
the metal film from all areas except current conducting area 101a
and piezoelectric areas 101b and 101c. In this case, the current
flows through the top and bottom metal film of current conducting
area 101a.
Alternatively, in order to make sensing sheet 101, one could start
with a single sheet of PVDF and apply metal film to the top and
bottom surface of current conducting area 101a and piezoelectric
areas 101b and 101c only, and then pole piezoelectric areas 101b
and 101c. As another approach to making sensing sheet 101, a
separate material such as a thin sheet of copper or aluminum could
be used for current conducting area 101a, and this material could
then be attached to PVDF sheets in bonding areas 101d and 101e
using heat fusing, adhesives, or mechanical means such as sewing.
Other methods of producing sensing sheet 101 will be apparent to
those of ordinary skill in the art who read the instant
disclosure.
FIG. 4 and FIG. 5 are different views showing an exemplary
embodiment of a large area magnetic field sensor of the present
invention. Magnetic flux sensor 1000 includes a sensing sheet 101
and a tension-producing housing 121. Thus incorporated in inventive
sensor 100 is a sensing sheet 101 such as shown in FIG. 2. Housing
121 provides support, protection, mechanical isolation, and
shielding for sheet 101.
Housing 121 includes attachment bars 102, springs 103, support bars
104, shields 105, current bars 106, case 107, and measurement
window 108. Attachment bars 102 connect each side of sensing sheet
101 to springs 103, which apply tension from corresponding support
bars 104. Tensile forces T.sub.1 and T.sub.2 are shown in FIG. 2
and FIG. 3. Springs 103.sub.1 exert tensile forces T.sub.1 upon
piezoelectric area 101b; springs 103.sub.2 exert tensile forces
T.sub.2 upon piezoelectric area 101c. Shields 105 above and below
piezoelectric areas 101b and 101c are made of highly conductive
material, such as aluminum or copper, and attenuate electromagnetic
fields that could induce electrical noise in the measurement
signal. Case 107 is also made of conductive material and attenuates
electromagnetic fields as well as providing mechanical support to
all components. Measurement window 108 is made of non-conductive
material, such as Vinyl, which allows magnetic fields to pass
through. Measurement window 108 protects sensing sheet 101 from
contact and prevents impingement of air currents, which would
contaminate the measurement signal.
The mass of attachment bars 102 and shields 105, along with the
springs 103, provide a mechanical isolation system for sensing
sheet 101. Vibrations in case 107 will be attenuated by this
mass-spring system before passing to sensing sheet 101. The mass
also provides an inertial impedance to support tension changes in
piezoelectric areas 101b and 101c. As current conducting area 101a
oscillates and applies forces to one side of piezoelectric areas
101b and 101c, the other side is prevented from moving by the
inertial reaction of the mass of attachment bars 102 and shields
105.
Two current bars 106, both shown in FIG. 4 and one shown
transparently in FIG. 5, provide current into and out of current
conducting area 101a. Current bars 106 are lengthwise opposite each
other, each current bar 106 situated along a widthwise edge of
current conducting area 101a. The resistance of current bars 106 is
very low compared to the resistance of current conducting area
101a. Therefore, the voltage is nearly uniformly across the width
of current conducting area 101a, and current flows uniformly down
the length.
FIG. 6 illustrates exemplary circuitry of the present invention.
The oscillator 500 produces a repeating waveform signal, such as a
sine wave or square wave, which is passed to a current amplifier
200, which produces oscillating current that passes down the length
of current conducting area 101a. The current interacts with
magnetic flux passing through current conducting area 101a, and
produces transverse forces on piezoelectric areas 101b and 101c,
which produce voltages according to the piezoelectric effect. In
this example, piezoelectric areas 101b and 101c are wired in series
with bottom electrode 101b.sub.BOT connected to bottom electrode
101c.sub.BOT and with top electrode 101b.sub.TOP and top electrode
101 crop producing the output so that fluctuating transverse forces
produce additive voltage. Piezoelectric areas 101b and 101c could
equally be wired anti-parallel with bottom electrode 101b.sub.BOT
connected to top electrode 101c.sub.TOP and with bottom electrode
101c.sub.BOT connected to top electrode 101b.sub.TOP so that
fluctuating transverse forces produce additive charge. For both the
series and the anti-parallel connection, noise sources such as air
currents, vertical vibration, temperature changes, etc. will
produce voltages of the same polarity on piezoelectric areas 101b
and 101c and therefore will cancel without contributing to total
voltage.
The total voltage produced by the combination of piezoelectric
areas 101b and 101c is amplified by the sense amplifier 300, which
for exemplary inventive practice is preferably a charge amplifier.
Resistor R acts as a filter when combined with the capacitance of
the piezoelectric areas 101b and 101c, and attenuates low frequency
signals. The sense amplifier 300 passes the voltage signal to the
demodulator 400, which also receives the repeating waveform signal
from the oscillator 500. The demodulator 400 produces an output
voltage that is proportional to the transverse force and is
therefore proportional to the total magnetic flux through the
current conducting area 101a.
A computer 600 can be implemented in communication with demodulator
400. As shown in FIG. 6, computer 600 receives output voltage
signals V from demodulator 400. Computer 600 processes the
electrical output voltage signals V. For instance, computer 600 can
apply calibration factors to output voltage signals V and display
data in engineering units for the benefit of the inventive
practitioner.
The present invention, which is disclosed herein, is not to be
limited by the embodiments described or illustrated herein, which
are given by way of example and not of limitation. Other
embodiments of the present invention will be apparent to those
skilled in the art from a consideration of the instant disclosure,
or from practice of the present invention. Various omissions,
modifications, and changes to the principles disclosed herein may
be made by one skilled in the art without departing from the true
scope and spirit of the present invention, which is indicated by
the following claims.
* * * * *